This invention relates to improved thermosetting powder paints and more particularly pertains to single component polymeric glycoluril prepolymers adapted to be self cross-linking with reactive hydroxyl, carboxyl, or amide groups on the same polymer upon exposure to heat; and further relates to concurrently, commonly assigned U.S. Ser. No. 49,220 pertaining to two-component thermosetting powder paints based on a polymeric glycoluril cross-linking component.
Powder paints are ordinarily manufactured from raw batch ingredients comprising resinous binders, opacifying and filler pigmentary solids, plasticizers, and other additives to provide opacity, good film properties, and adhesion to substrates. The raw batch ingredients are uniformly mixed, formed into coherent extrudate by hot extrusion, and then comminuted to form small particle powder paints which are ordinarily free flowing at normal room temperature. Powder paints usually are uniform small powders passing 325 mesh or less than about 44 microns. Powder paints contain little or no fugitive solvents and depend upon their own inherent characteristics of the powder to melt, level, coalesce, and fuse to form an attractive coherent film on the substrate. The powder must not fuse in the container and cannot be subjected to cold flow so as to maintain individual powder particles prior to use. Recently issued U.S. Pat. No. 4,118,437 and U.S. Pat. No. 4,064,191 disclose thermosetting powder coatings wherein the cross-linking component is an alkylated glycoluril derivative.
Thermosetting powder paints are particularly suitable for use in commercial industrial process particularly since powder paints are essentially free of organic solvents. Prior art powder coatings ordinarily are based on two-component systems wherein the two components are adapted to coreact upon exposure to heat. Two-component systems, however, have inherent deficiencies such as reproducibility problems and quality control problems due to homogenization of dissimilar materials, incompatibility of two components causing curing and film surface problems, difficulty in controlling tack temperatures and/or melt temperatures and often undesirably depressed due to mixing two solid materials as well as higher cost, inconvenience, higher risk and other errors related to mixing two dissimilar materials wherein one of the materials is a monomeric or other low molecular weight material. Present commercial powder coatings often exhibit poor weathering properties. These disadvantages are avoided and many other advantages can be achieved by the one-component self-curing power coating composition of this invention.
It now has been found that a single component self-curing matrix polymer binder of this invention advantageously avoids problems inherent in two-component systems and provides an efficient powder coating adapted to fuse and cure into a continuous surface film exhibiting excellent film integrity properties. The self-curing single component matrix polymer is a moderately low molecular weight polymer synthesized by acid catalyzed condensation of a tetra-alkoxy methyl and/or tetramethylol glycoluril with a poly hydroxy material. The methylol and/or alkoxy methyl groups are coreactive with preferably hydroxyl groups upon exposure to curing temperatures to provide a cross-linked thermoset cured powder coating. The merits and advantages of this invention will become more apparent from the Detailed Description of the Invention.